Prefabricated homes gaining popularity in Sonoma County

When Carol and Will Ashford lost their Santa Rosa home in the devastating Tubbs Fire five years ago, they knew the road to rebuilding would be rocky.

The demand and cost for qualified contractors was sky-high. The wildfire may have consumed everything, but the land they loved, with its beautiful vistas, remained. They wanted to return.

The couple opted to streamline the rebuilding process by going for a factory-built home that could be lifted into place. They reached out to St. Paul, Minnesota, architect Geoffrey Warner of Alchemy, known for its sustainable modern designs.

Warner already had received accolades for his Sonoma weeHouse, a minimalist, 640-square-foot corrugated Cor-Ten steel box with 9-foot sliding glass walls and a matching guest cottage half its size. It was built in an Oregon factory and trucked to Sonoma Mountain as a family getaway for Apple’s director of store design.

The Sonoma weeHouse was featured by many design writers, including in Dwell magazine, and had received a Small Project Award from the American Institute of Architects, among other awards.

The Ashfords were drawn to Alchemy’s experience with sustainable modern design, said author Sheri Koones, who chose to include the Ashfords’ house in her latest coffee table book: “Prefabulous for Everyone.”

Koones, who has written a series of design books featuring prefabricated homes and has watched the industry evolve over more than 20 years, culled through hundreds of candidates before selecting 23 homes to profile. They represent a variety of construction methods and materials, including modular, structural insulated panels (SIPS), prefab metal framing, insulated concrete forms (ICFs), post-and-beam framing and kit houses.

The weeHouse Alchemy built for the Ashfords is one of several prefab homes in the book that replaced homes lost to natural disasters. They include a Malibu home that replaced a home lost to the Woolsey Fire in 2018 and a 1,900-square-foot villa in the Virgin Islands that replaced a home decimated by major back-to-back hurricanes in 2017.

Responding to natural disasters

The Ashfords’ house was built in the Plant Prefab factory in Rialto, near San Bernardino. The company claims to build homes twice as fast as regular on-site construction and at a lower cost by requiring less labor and incurring less building waste. Many of their homes leave the factory 90% complete.

Koones said there is a tremendous need for “ingenuity” in developing new housing to replace homes lost to natural disasters. Prefab is an attractive, reasonably priced option.

“This was an interesting project because they rebuilt it after a fire and they needed a house fairly quickly. And Plant Prefab was able to do that,” Koones said. “And they used a lot of methods that will prevent it, hopefully, from being burned down again.

The Ashford weeHouse consists of three modular units set on a concrete plinth, which, hopefully, will keep windblown embers from igniting the house at the base of the wall.

The exterior material on the modules is metal. While not fireproof, metal can act as a “first layer of defense” against flying embers, Koones pointed out.

Behind the siding and ceiling is continuous, ceramic-faced fire-resistant sheathing. Cantilevered soffits are covered in a fire-resistant, fly-ash composite. The decking is made of IPE, a high-density hardwood with a class A fire rating, which means it does not burn well and likely won’t add fuel to a fire.

“I think it’s just a beautiful design and very open in many areas to the outside, to bring the outside in,” Koones said.

Extra space

Prefab is taking off in both the East Coast and the West, where labor and housing costs are high. It’s also popping up in Koones’ home city of Greenwich, Connecticut, one of the wealthiest communities in the country.

There are multiple factors driving the demand for faster and more efficient housing construction, she said, including the growing popularity of accessory dwelling units, or ADUs.

Previously known as granny units or guesthouses, they can provide more affordable housing in high-cost places like Sonoma County. They can bring homeowners additional income to help cover mortgage payments. They also can allow older people to age in place by providing space for a caregiver or for multiple generations to live close but not necessarily under the same roof.

Koones profiles a couple of ADUs, including a house in Seattle built from a custom-designed kit by Lindal Cedar Homes. It packs a lot into its maximum allowed size of nearly 1,000 square feet, with clerestory windows and wood beams on the ceilings. It’s built with many of the same interior materials as the main house.

Prefabricated homes have improved immensely in both design and quality in the past 20 years. Koones said they offer an attractive option to younger people and families who can’t afford the McMansions of an earlier day, or purposely want to live lighter.

For older empty nesters or people who don’t want to maintain a big family house any longer, more compact manufactured homes are more efficient and freeing, she said.

“The market is changing, and attitudes about housing are changing. And as it’s changed, I’ve been doing books that are in touch with what’s going on in the world,” said Koones, whose series of books have chronicled that evolution: “Prefabulous,” “Prefabulous Small Houses,” “Prefabulous + Sustainable,” “Prefabulous + Almost Off the Grid” and “Prefabulous World,” which showcases prefabricated homes across the globe.

Her next book will focus on prefabricated ADUs.

“There are more ADUs in California than the rest of the country put together, and California is the only state that has universal acceptance of ADUs. Throughout the entire state of California, you can put in ADUs,” she said.

In “Prefabulous for Everyone,” Koones sought to profile homes that would be within economic reach of a large range of people, and offer energy efficiency and other green building features.

The Ashford home in Santa Rosa has passive cooling through ventilating skylights with sun and rain sensors. There are low-flow faucets, natural oil floor coating, a south-side pergola to control sun exposure (it doubles as a rack for solar panels). An energy-efficient, mini-split heat pump allows for zones of heating and cooling in the house.

One very inexpensive home in the book is the petite, 375-square-foot Boxabl Casita, a modular home in Las Vegas made of structural insulated panels (SIPs). Boxabl company founder Paulo Tiramini’s aim is to mass-produce in factories homes that are built fast, strong and of high quality and low cost.

“He’s sold about 100,000 and he has a back-order of about 100,000 units,” Koones said of the tiny homes, which start at about $60,000.

“What’s interesting about it is it has a full bathroom and a full kitchen. It’s very clever the way they are designed. This is not something a lot of people might want to live in, but it is as big or bigger than some of the small apartments that kids are living in today,” she said.

Koones said this type of prefabricated home could be useful for a lot of purposes, from housing for the homeless to emergency housing for refugees.

“Prefab works well for any structure,” Koones said. “It’s even being used today liberally in commercial real estate. I think the world is becoming much more accepting of it. When I first started writing about it, they were these little tacky houses. And today they’re as beautiful and as special as any other site-built house.”

You can reach Staff Writer Meg McConahey at 707-521-5204 or meg.mcconahey@pressdemocrat.com.